Method for operating an internal combustion engine of a vehicle, especially a motor vehicle, and device for implementing said method

ABSTRACT

The invention relates to a method for operating an internal combustion engine of a vehicle, particularly a motor vehicle, wherein the nitrogen content in an intake air flow ( 1 ) suctioned from the ambient air is reduced before delivering the air flow to at least one combustion chamber of the internal combustion engine ( 7 ) in order to produce a nitrogen-reduced combustion air flow whose oxygen content is higher than that of the suctioned air flow. According to the invention, the suctioned air flow ( 1 ) is run past or along at least one porous solids body ( 5 ) in at least one partial area of the intake air flow path ( 3 ), the size of the pores of said solids body being designed in such a way that the quantity of nitrogen molecules drawn off from the intake air flow ( 1 ) through the porous solids wall ( 5 ) is larger than the quantity of oxygen molecules drawn off from the oxygen or nitrogen molecules of the intake air flowing past the porous solids body ( 5 ) in order to form the nitrogen-reducing and oxygen-enriched combustion air flow that is supplied to the at least one combustion chamber ( 7 ) as main partial gas flow ( 8 ) and at least one nitrogen-enriched and oxygen-reduced secondary partial gas flow ( 9 ) which is not delivered to the at least one combustion chamber ( 7 ).

The invention relates to a method for operating an internal combustion engine of a vehicle, especially a motor vehicle, as specified in the preamble of claim 1, and to a device for implementing said method as specified in the preamble of claim 11.

Pretreatment of ambient air introduced into a combustion chamber of an internal combustion engine as combustion air, which usually is made up of 21% oxygen, 78% nitrogen and 1% residual gas, for reduction of the pollutant components of the internal combustion engine is generally known. For example, DE 197 10 840 A1 has disclosed provision of an enrichment channel communicating with an intake channel, a membrane permeable by oxygen molecules being mounted in the enrichment channel. As a result of the partial vacuum predominating in the intake channel, ambient air is drawn through the membrane and is subsequently enriched with oxygen on the outlet side. In the area of opening of the enrichment channel into the intake channel the ambient air normally drawn in is admixed with the oxygen-enriched air coming from the enrichment channel before this air is introduced into the combustion chamber as combustion air.

DE 195 43 884 A1 discloses a process in which an oxygen-enriched volume flow is obtained as permeate in a complex process in a noncryogenic separation unit from an air volume flow and is introduced into the internal combustion engine. The oxygen-enriched volume flow from the noncryogenic separation unit is compressed and temporarily stored in a buffer tank from which it is taken as needed.

DE 197 10 842 A1 discloses a process for reduction of pollutants and combustion exhaust gases of internal combustion engines, a process in which combustion air of increased oxygen content is introduced into the internal combustion engine, the combustion air being obtained from ambient air by a membrane mounted in a chamber and being permeable only by oxygen molecules. In order to reduce the light-off time of the catalytic converter so as to permit reduction of the toxic emission downstream from the catalytic converter, the application proposes that the gas with an increased oxygen component be admixed with the intake air as a function of the operating point of the internal combustion engine.

DE 199 12 137 A1 discloses an internal combustion engine with oxygen enrichment such that the internal combustion engine has a gas accumulator for storage of oxygen-enriched gas which has been produced, means being provided for delivery of oxygen-enriched gas to the internal combustion engine during a cold-start phase until a specified warm-air operating state of the internal combustion engine has been reached. When the internal combustion engine is in warmed-up operation, temporarily oxygen-enriched gas is produced from air by means of an oxygen separation unit and stored at least for a brief period in the gas accumulator.

A process and structure similar to that of DE 197 10 840 A1 have also been disclosed in DE 44 04 681 C1, in which at least one channel conducting the oxygen-nitrogen air mixture is associated with an exhaust gas channel connected to the combustion chamber, is provided with a partition permeable by oxygen or stores oxygen, and oxygen is delivered exclusively by way of it to the combustion exhaust gas of a combustion chamber.

DE 42 01 423 A1 discloses a process in which a complex gas permeation system is mounted upstream from a diesel internal combustion engine so that the combustion air conducted to the diesel internal combustion engine is first filtered in its entirety through a membrane for generation of an oxygen-enriched combustion air flow.

Another generic process for operation of an internal combustion engine of a motor vehicle is disclosed in WO 01/18369 A1. Specifically, a nitrogen absorber is provided in this instance as gas separation unit, but it is very costly and complex in structure. In this instance the oxygen-enriched gas is then admixed, again by way of a separate channel, with the non-oxygen-enriched combustion air drawn in from the ambient atmosphere.

All these conducts of the process and structures have in common the feature that oxygen-enriched air is admixed with the air stream drawn in from the ambient air by way of a separate delivery channel or the combustion air drawn in is filtered in its entirety through a membrane for the purpose of enrichment with oxygen prior to delivery to the combustion chamber. Such structures present the problem that, in the first instance, a high equipment-engineering and civil engineering effort is required and, in the second instance, the danger exists that membranes may at some point in time become clogged so that delivery to the combustion chamber of the air flow required is no longer guaranteed. Conversion and application for use in series is accordingly difficult in this case.

The object of the invention is to make available a process for operation of an internal combustion engine of a vehicle, a motor vehicle in particular, and a device for implementation of such a process, a process and device by means of which oxygen enrichment of combustion air introduced into a combustion chamber of the internal combustion engine may be effected by simple means dependable in operation.

This object is attained with respect to the process by the characteristics specified in claim 1.

Claim 1 specifies that the intake air flow is conducted over at least one partial area of the intake flow air path past and/or along at least one porous solid-state wall, the size of the pores of which is configured so that, of the oxygen and nitrogen molecules flowing past along the porous solid-state wall, a greater number of nitrogen molecules than of oxygen molecules pass through the porous solid-state wall. This results in formation of at least one nitrogen-reduced and oxygen-enriched combustion air flow which may be introduced into the at least one combustion chamber as primary gas flow component and results in formation of at least one nitrogen-enriched and oxygen-reduced secondary gas flow which is not introduced into the at least one combustion chamber.

Of particular advantage of this conduct of the process claimed for the invention is accordingly the more or less casual possibility of branching nitrogen off an essentially unimpeded primary air flow as intake air flow, since the porous solid-state walls effecting oxygen enrichment are mounted along the path of flow of the intake air in such a way that this flowing past or sweeping past of the intake air suffices to effect oxygen enrichment and accordingly nitrogen reduction in the combustion air flow introduced into the combustion chamber. That is to say, in the solution claimed for the invention, the flow of the combustion air drawn in is essentially unimpeded, while in the prior art as disclosed measures are taken which as a whole impair the flow of air to the combustion chamber or modify it, for example, by use of membranes or filters blocking the path of flow, ones through which the combustion air drawn in must flow in its entirety and which may clog with the passage of time. In addition, no additional equipment engineering structures such as gas reservoirs or additional air circulation ducts are required by means of which oxygen-enriched gas produced in a separate unit must be admixed with a flow of intake air. Consequently, conduct of the process claimed for the invention makes certain that everything which is drawn in may also flow in the direction of the combustion chamber.

Tests have shown that at a given temperature the nitrogen molecules move at a higher speed than do the oxygen molecules, which are heavier than the nitrogen molecules. As a result of these different speeds, when the molecules strike the porous solid-state wall, the nitrogen molecules can pass through the porous solid-state wall with greater ease and more rapidly than can the oxygen molecules. These different transport and velocity properties of the nitrogen molecules and oxygen molecules are accordingly used to advantage in an especially simple way in order to effect nitrogen reduction in the intake air in order to configure a nitrogen-reduced and oxygen-enriched combustion air flow in the intake air without the need for complex admixture of oxygen-rich gas flows or filtering of the air flow as a whole through membranes or the like affecting the flow pattern. It is claimed for the invention that the oxygen enrichment is as it were coincidental.

In addition, such conduct of the process in conjunction with operation of an internal combustion engine may result in reduction of the raw emissions of nitrogen oxide, and of carbon monoxide, hydrocarbon, and soot particles as well. Reduction of the pollutants emitted in turn results in smaller dimensions of parts of the exhaust gas system, something which in its turn results in lower production costs.

Especially advantageous results can be obtained by compressing the intake air flow as specified in claim 2 by means of at least one compressor prior to its delivery to the porous solid-state wall. As an alternative or in addition, however, provision may be made as specified in claim 3 such that the secondary partial gas flow is exhausted in the area of the porous solid-state wall by means of a vacuum device. This higher pressure level supports nitrogen molecule reduction of the air intake flow, a pressure difference provided as specified in claim 4 being generated in the direction of the secondary partial gas component flow side on the primary partial gas flow side and the secondary partial gas flow side.

In another especially preferred conduct of the process as provided in claim 5, the secondary partial gas flow may be directed back at least in part to the intake air flow before its is introduced into the solid-state wall area, if this is found to be necessary.

In one also especially preferred conduct of the process as specified in claim 6, a partial exhaust gas flow of an exhaust gas flow withdrawn downstream from the combustion chamber is introduced into the nitrogen-reduced and oxygen-enriched combustion air flow is introduced into the at least one combustion chamber. The volume of the exhaust gas flow may be reduced to advantage by an advantageous circulation system such as this, as a result of which, for example, the converters, such as a three-way catalytic converter, an oxy-catalytic converter, and a particle filter, may also be made smaller, so that the dimensions of the exhaust gas system as a whole may be made smaller. And, again, costs may be lowered as a result. In addition, it is possible by simple means to employ gases distinguished by an especially high heating value and in addition having no nitrogen or nitrogen oxide components to assign a desired combustion air composition, for example, in conjunction with control action. For example, as specified in claim 7, provision may be made such that there is introduced into the nitrogen-reduced combustion air flow in normal operation of the internal combustion engine an amount of partial exhaust gas flow such that the oxygen component of the primary partial gas flow, that is, of the nitrogen-reduced combustion air flow, corresponds essentially to the intake air flow drawn in from the ambient atmosphere, the oxygen component in this instance being around 21%. As an alternative, however, as specified in claim 8 provision may also be made such there is introduced into the nitrogen-reduced combustion air flow in startup operation of the internal combustion engine, that is, during a cold start, an amount of partial exhaust gas flow such that the oxygen component of the primary partial gas flow, that is, the nitrogen-reduced combustion air flow, is greater than the oxygen component of the intake air flow drawn in from the ambient atmosphere. By preference the oxygen component in this instance may fall within the range, for example, of 21 to 40%. The efficiency of the engine in burning of the mixture may be increased for a brief period by such oxygen enrichment without the risk that conventional internal combustion engines might not be able to withstand the higher combustion temperatures which might occur. In theory, however, appropriate dimensioning and design of the engines would be possible in such a case, so that the internal combustion engine could be operated even over a lengthy period with an increased oxygen component.

Special preference is also to be given as specified in claim 9 to implementation of the process in which the amount of partial exhaust gas flow introduced into the air intake flow is controlled as a preset value by a control device as a function of an assigned oxygen component in the combustion air flow. It is this control device which is to compute and/or determine the actual oxygen component of the intake air flow directly and/or indirectly as the actual value. Such control permits especially simple and rapid compensation for any lower air density, such as in mountainous regions or at elevated exterior temperatures.

In another preferred conduct of the process as specified in claim 10 provision is also made such that the partial exhaust gas flow introduced into the intake air stream is established so that in the at least one combustion chamber a combustion air flow with more or less constant gas volume is available for formation of a mixture with a fuel. This ensures that a more or less constant gas volume is drawn into the combustion chamber each time for the purpose of continuous combustion.

The object of the device is attained by the characteristics specified in claim 11. The advantages indicated in the foregoing in connection with the process apply to the device as well, so that they will not be discussed further at this point.

The invention will be described in detail below with reference to the drawing, in which the sole FIGURE illustrates in diagram form conduct of the process claimed for the invention, with an intake air flow 1 which is drawn in from the ambient atmosphere, is compressed in a compressor 2, and subsequently flows, at a pressure p1, which is higher than atmospheric pressure, past or along a porous solid-state wall 5 of a reduction device 4. The porous solid-state wall 5 has a pore size of the pores 6 such that, of the nitrogen and oxygen molecules of the intake air flowing along the porous solid-state wall 5, a higher number of nitrogen molecules of the air intake flow than oxygen molecules flow through the porous solid-state wall 5 from the air intake flow. There is thereby formed along the primary flow path both a nitrogen-reduced and oxygen-enhanced combustion air flow which may be introduced into the internal combustion engine 7 and a nitrogen-enriched and oxygen-reduced secondary partial gas flow 9 which is not introduced into the internal combustion engine 7. A pressure level p2 lower than the higher pressure level p1 assigned by the compressor 2 in the area of the intake air flow path 3 as primary flow direction predominates in the secondary partial gas flow 9.

As is indicated by broken lines in the FIGURE, the secondary gas flow or flows 9 optionally may also be reintroduced into compressor 2 in circulation.

The nitrogen-reduced and oxygen-enriched primary partial gas flow 8 leaving the reduction device 4 is then conducted as combustion air flow to a combustion chamber of the internal combustion engine 7. As is also illustrated in greatly simplified diagrammatic form in the FIGURE, a partial exhaust gas flow 11 withdrawn from the exhaust gas flow 10 may, in conjunction with a control device 12 shown here in diagrammatic form only, be returned to the primary partial gas flow 8 by means of partial exhaust gas return for the purpose, for example, of constantly introducing in normal operation of the internal combustion engine 7 a partial exhaust gas flow amount into the nitrogen-reduced combustion air flow as primary gas flow such that the oxygen component of the primary partial gas flow 8 corresponds approximately to that of the intake air flow 1 drawn from the ambient atmosphere, that is, in this instance amounts essentially to 21%. The admixing may in this instance be effected in an admixture device 13.

As an alternative, however, during start up operation, that is, for example, during cold starting of the internal combustion engine 7, an amount of partial exhaust gas flow may be introduced into the primary partial gas flow 8 such that the oxygen component of the primary partial gas flow 8 is greater than the oxygen component of the intake air flow drawn from the ambient atmosphere, that is, may be greater than 21%. The amount of partial exhaust gas flow 11 introduced into the primary partial gas flow 8 is controlled as preset value by means of the control device 12, which directly or indirectly calculates and/or determines the actual oxygen component in the primary partial gas flow 8 as an actual value, for example, by means of a conventional oxygen probe, which is not shown here. 

1. A method for operating an internal combustion engine of a vehicle, comprising: reducing a nitrogen component of an intake air flow drawn from ambient atmosphere is before being introduced into at least one combustion chamber of the internal combustion engine for the purpose of generating a nitrogen-reduced combustion air flow the oxygen component of which is higher than that of the intake air flow drawn in, wherein the intake air flow is guided along at least one partial area of the intake air flow path past and/or along at least one porous solid-state wall the pore size of which is designed so that a greater number of nitrogen molecules of the oxygen and nitrogen molecules of the intake air flowing along the porous solid-state wall than of oxygen molecules moves through the porous solid state wall for formation for the nitrogen-reduced and oxygen-enriched combustion air flow as primary partial gas flow which may be introduced into the at least one combustion chamber and at least one nitrogen-enriched and oxygen-reduced secondary partial gas flow which is not introduced into the at least one combustion chamber.
 2. The process as claimed in claim 1, wherein the intake air flow is compressed by at least one compressor before it is delivered to the solid-state wall.
 3. The process as claimed in claim 1, wherein the secondary partial gas flow is exhausted in the area of the porous solid-state wall by means of a vacuum device.
 4. The process as claimed in claim 2, wherein the pressure (p1) on the primary partial gas flow side higher than the pressure (p2) on the secondary partial gas flow side.
 5. The process as claimed claim 1, wherein the secondary partial gas flow is returned at least in part to the intake air flow prior to delivery of the intake air flow to the solid-state wall area.
 6. The process as claimed in claim 1, wherein a partial exhaust gas flow of an exhaust gas flow is introduced into the nitrogen-reduced and oxygen-enriched combustion gas flow before such combustion gas flow is introduced into the at least one combustion chamber.
 7. The process as claimed in claim 6, wherein there is introduced into the nitrogen-reduced combustion air flow as primary partial gas flow in normal operation of the internal combustion engine an amount of partial secondary exhaust gas flow such that the oxygen component of the primary partial gas flow corresponds essentially to the intake air flow drawn from the ambient atmosphere, the oxygen component being essentially 21%.
 8. The process as claimed in claim 6, wherein there is introduced into the nitrogen-reduced combustion air flow as primary partial gas flow in startup operation of the internal combustion engine an amount of partial exhaust gas flow such that the oxygen component of the primary partial gas flow is greater than the oxygen component of the intake air flow drawn from the ambient air.
 9. The process as claimed in claim 1, wherein the amount of the partial exhaust gas flow introduced into the primary partial gas flow is controlled as a preset value as a function of a specified oxygen component of the primary partial gas flow by means of a control device which indirectly or directly calculates and/or determines the actual oxygen component of the primary partial gas flow as the actual value.
 10. The process as claimed in claim 9, wherein the partial exhaust gas flow introduced into the intake air flow is additionally established in such a way that a combustion air flow is available in the at least one combustion chamber as primary partial gas flow of more or less constant gas volume per cycle for formation of a mixture with a fuel.
 11. A device for implementing a method for operating an internal combustion engine of a vehicle, in particular as specified in one of claims 1 to 10, comprising: a reduction device for reduction of nitrogen in an intake air flow drawn from the ambient atmosphere for production of a nitrogen-reduced combustion air flow the oxygen component of which is higher than that of the intake air flow, wherein the reduction device is in the form of at least one porous solid-state wall extending along at least one partial area of the flow path of the intake air flow, and in that the porous solid-state wall is of a pore size such that, of the nitrogen and oxygen molecules of the intake air flowing along the porous solid-state wall, a greater number of nitrogen molecules than of oxygen molecules move through the porous solid-state wall from the intake air flow, in such a way that a nitrogen-reduced and oxygen-enriched combustion air flow may be introduced into the at least one combustion chamber.
 12. The process as claimed in claim 6, wherein there is introduced into the nitrogen-reduced combustion air flow as primary partial gas flow in startup operation of the internal combustion engine an amount of partial exhaust gas flow such that the oxygen component of the primary partial gas flow is greater than the oxygen component of the intake flow drawn from the ambient air, ranging from 21% to 40%. 